U.S. patent application number 15/962420 was filed with the patent office on 2018-08-23 for systems and methods for parallel channel microfluidic separation.
The applicant listed for this patent is The Charles Stark Draper Laboratory, Inc. Invention is credited to Jason Oliver Fiering, Hoi-Cheong Steve Sun.
Application Number | 20180236159 15/962420 |
Document ID | / |
Family ID | 63166315 |
Filed Date | 2018-08-23 |
United States Patent
Application |
20180236159 |
Kind Code |
A1 |
Fiering; Jason Oliver ; et
al. |
August 23, 2018 |
SYSTEMS AND METHODS FOR PARALLEL CHANNEL MICROFLUIDIC
SEPARATION
Abstract
The present disclosure describes a system and method for
microfluidic separation. More particularly, the disclosure
describes a system and method for the purification of a fluid by
the removal of undesired particles. The device includes
microfluidic separation channels that include multiple outlets. The
device also includes isolation slots positioned between each of the
microfluidic separation channels. The device's base includes
multiple acoustic transducers which in some implementations are
configured to protrude into the isolation slots. The acoustic
transducers are configured to generate aggregation axes within the
separation channels, which are used to separate out undesired
particles.
Inventors: |
Fiering; Jason Oliver;
(Boston, MA) ; Sun; Hoi-Cheong Steve; (Tampa,
FL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Charles Stark Draper Laboratory, Inc |
Cambridge |
MA |
US |
|
|
Family ID: |
63166315 |
Appl. No.: |
15/962420 |
Filed: |
April 25, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14815501 |
Jul 31, 2015 |
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15962420 |
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62489560 |
Apr 25, 2017 |
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62031662 |
Jul 31, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61M 2205/3673 20130101;
A61M 1/362 20140204; A61M 1/365 20140204; B01D 21/283 20130101;
A61M 1/3678 20140204 |
International
Class: |
A61M 1/36 20060101
A61M001/36; B01D 21/28 20060101 B01D021/28 |
Claims
1. A separation device comprising: a first substrate comprising: a
first plurality of microfluidic channels defined in a first face of
the first substrate, wherein each of the first plurality of
microfluidic channels comprise an upstream portion and a downstream
portion; a second plurality of microfluidic channels defined in a
second face of the first substrate, wherein each of the second
plurality of microfluidic channels comprise an upstream portion and
a downstream portion; and a plurality of via channels coupling the
downstream portion of the first plurality of microfluidic channels
to the upstream portion of the second plurality of microfluidic
fluid channels; a second substrate coupled with the first face of
the first substrate, the second substrate defining a wall of the
first plurality of microfluidic fluid channels; and a third
substrate coupled with the second face of the first substrate, the
third substrate defining a wall of the second plurality of
microfluidic fluid channels, wherein at least one of the first
substrate, the second substrate, and the third substrate are
configured to couple with a base substrate comprising one or more
acoustic transducers.
2. The device of claim 1, wherein the first substrate comprises an
isolation slot positioned between each of the first plurality of
microfluidic fluid channels.
3. The device of claim 2, wherein each of the one or more acoustic
transducers protrude perpendicular to a face of the base substrate
and into the isolation slot positioned between each of the first
plurality of microfluidic fluid channels.
4. The device of claim 2, wherein the isolation slot positioned
between each of the first plurality of microfluidic fluid channels
run substantially parallel to and the entire length of the first
plurality of microfluidic channels.
5. The device of claim 1, further comprising the base substrate
comprising the one or more acoustic transducers, each of the one or
more acoustic transducers coupled with the second face of the first
substrate.
6. The device of claim 1, wherein the downstream portion of the
each of the first plurality of microfluidic fluid channels further
comprises a first outlet positioned substantially along a
longitudinal axis.
7. The device of claim 1, wherein the downstream portion of the
each of the first plurality of microfluidic fluid channels further
comprises a second outlet positioned adjacent to a lateral wall of
a first outlet positioned substantially along a longitudinal
axis.
8. The device of claim 1, wherein the first substrate defines a
manifold configured to distribute a fluid to the first plurality of
microfluidic fluid channels.
9. The device of claim 8, wherein the manifold comprises a network
of biomimetic channels.
10. The device of claim 8, wherein a distribution portion of the
manifold is defined in the first face of the first substrate and a
collection portion of the manifold is defined in the first face and
the second face of the first substrate.
11. The device of claim 10, wherein a portion of the collection
manifold defined in the second face of the first substrate are
fluidically connected to the collection portion of the manifold
defined in the first face of the first substrate by the plurality
of via channels.
12. The device of claim 1, wherein each of the first plurality of
microfluidic channels further comprise: a first wall having a first
thickness; and a second wall opposite the first wall and having a
second thickness.
13. The device of claim 12, wherein the second thickness is
different than the first thickness.
14. A method comprising: providing a fluid cleansing device
comprising: a first substrate comprising: a first plurality of
microfluidic channels defined in a first face of the first
substrate, wherein each of the first plurality of microfluidic
channels comprise an upstream portion and a downstream portion; a
second plurality of microfluidic channels defined in a second face
of the first substrate, wherein each of the second plurality of
microfluidic channels comprise an upstream portion and a downstream
portion; and a plurality of via channels coupling the downstream
portion of the first plurality of microfluidic channels to the
upstream portion of the second plurality of microfluidic fluid
channels; a second substrate coupled with the first face of the
first substrate, the second substrate defining a wall of the first
plurality of microfluidic fluid channels; and a third substrate
coupled with the second face of the first substrate, the third
substrate defining a wall of the second plurality of microfluidic
fluid channels, wherein at least one of the first substrate, the
second substrate, or the third substrate are configured to couple
with a base substrate comprising one or more acoustic transducers;
flowing a fluid comprising particles through the first plurality of
microfluidic channels; and directing, with an acoustic wave
generated by the one or more acoustic transducers, the particles to
a first aggregation axis of each of the first plurality of
microfluidic channels.
15. The method of claim 14, further comprising flowing the fluid
through a manifold defined in the first substrate
16. The method of claim 15, wherein the manifold comprises a
network of biomimetic channels.
17. The method of claim 15, further comprising: flowing the fluid
through a distribution portion of the manifold defined in the first
face of the first substrate; and collecting at least a portion of
the fluid at a collection portion of the manifold defined in the
first face and the second face of the first substrate.
18. The method of claim 14, wherein the first substrate comprises
an isolation slot positioned between each of the first plurality of
microfluidic fluid channels.
19. The method of claim 18, wherein each of the one or more
acoustic transducers protrude perpendicular to a face of the base
substrate and into the isolation slot positioned between each of
the first plurality of microfluidic fluid channels.
20. The method of claim 14, further comprising selecting a
frequency of the acoustic wave based on a wall thickness of the
first substrate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit of priority under
35 U.S.C. .sctn. 120 as a continuation-in-part of U.S. patent
application Ser. No. 14/815,501 filed Jul. 31, 2015, which claims
the benefit of priority to U.S. Provisional Patent Application No.
62/031,662 filed on Jul. 31, 2014. This application also claims the
benefit of priority to U.S. Provisional Patent Application No.
62/489,560, filed Apr. 25, 2017. Each of the foregoing applications
are herein incorporated by reference in their entirety.
BACKGROUND
[0002] The concept of blood cleansing and separation has been tried
previously but remains laborious. Previous blood cleansing concepts
have included laboratory scale methods of centrifugation, capillary
electrophoresis, liquid chromatography, field flow fractionation,
and liquid-liquid extraction. These devices have failed to deliver
continuous flow cleansing devices. In addition to often discarding
large portions of the blood, current cleansing devices may rely on:
diluents, sheath flow, controlled solution conductivity, costly
microfabricated on-chip materials, and toxic additives.
[0003] Chimeric Antigen Receptor T-cell therapies (CAR-T) can use
genetically engineered I-cells re-infused into the patient to
recognize and kill cancer cells. The first step can be to isolate
the I-cells from a sample of the patient's blood. The blood sample
can typically be a 300-400 ml product enriched in white blood cells
(leukapheresis), which can still include only about 1% of the
target T-cells. The current isolation practice can involve
laborious centrifugal separation under highly controlled
conditions, which can damage the blood cells.
SUMMARY OF THE DISCLOSURE
[0004] The present solution can reduce costs and increase access to
life-saving therapy by purifying lymphocytes, including T-cells,
from patient blood samples. The present solution can acoustically
separate lymphocytes at rates of 2 ml/min or higher. The present
solution provides a polystyrene acoustophoretic device that can
accept standard leukapheresis product with only 1:1 dilution and is
tunable. In a high-recovery mode, the system can recover about 72%
of lymphocytes with 90.4% purity. In a high-purity mode, the system
can recover about 43% of lymphocytes with a 96.8% purity. The
performance of the present device can exceed that achieved by
existing centrifugal methods. The present solution can also achieve
between about 80% and about 90% red blood cell (RBC) separation at
rates between about 0.5 and about 2 mL/min.
[0005] As an overview, the multi-channel system can include
multiple channels separated by air gaps to substantially prevent
acoustic coupling of neighboring channels. The system can also
include distribution and collection manifolds that distribute blood
from a main inlet to each of the channels and collect the outflow
to two outlets. The two collection manifolds to the two outlet can
be fabricated on opposing faces of a substrate and connected by
holes penetrating the substrate.
[0006] According to one aspect of the disclosure a separation
device can include a first substrate, a second substrate, and a
third substrate. The first substrate can include a first plurality
of microfluidic channels that are defined in a first face of the
first substrate. Each of the first plurality of microfluidic
channels can include an upstream portion and a downstream portion.
The second plurality of microfluidic channels can be defined in a
second face of the first substrate. Each of the second plurality of
microfluidic channels can include an upstream portion and a
downstream portion. The first substrate can include a plurality of
via channels coupling the downstream portion of the first plurality
of microfluidic channels to the upstream portion of the second
plurality of microfluidic fluid channels. The second substrate can
be coupled with the first face of the first substrate. The second
substrate can define a wall of the first plurality of microfluidic
fluid channels. The third substrate can be coupled with the second
face of the first substrate. The third substrate can define a wall
of the second plurality of microfluidic fluid channels. The first,
second, or third substrate can be configured to couple with a base
substrate comprising one or more acoustic transducers.
[0007] The first substrate can include an isolation slot that is
positioned between each of the first plurality of microfluidic
fluid channels. Each of the one or more acoustic transducers can
protrude perpendicular to a face of the base substrate and into the
isolation slot positioned between each of the first plurality of
microfluidic fluid channels. The isolation slots can be positioned
between each of the first plurality of microfluidic fluid channels
run substantially parallel to and the entire length of the first
plurality of microfluidic channels. The device can also include the
base substrate that can include the one or more acoustic
transducers. Each of the one or more acoustic transducers can be
coupled with the second face (or other free face) of the first
substrate.
[0008] The downstream portion of the each of the first plurality of
microfluidic fluid channels can include a first outlet that is
positioned substantially along a longitudinal axis. The downstream
portion of the each of the first plurality of microfluidic fluid
channels can include a second outlet positioned adjacent to a
lateral wall of the first outlet. The first substrate can define a
manifold that is configured to distribute a fluid to the first
plurality of microfluidic fluid channels. The manifold can include
a network of biomimetic channels. A distribution portion of the
manifold can be defined in the first face of the first substrate
and a collection portion of the manifold can be defined in the
first face and the second face of the first substrate.
[0009] In some implementations, each of the plurality of
microfluidic separation channels also include a first wall that has
a first thickness and a second wall opposite the first wall that
has a second thickness. In some implementations, the first
thickness and the second thickness are equal to c.sub.s(f)/4f, or
an odd multiple thereof, where c.sub.s(f) is a frequency dependent
speed of a shear wave through the plastic.
[0010] In other implementations, the second thickness is different
than the first thickness. In some implementations, the first
thickness is about c.sub.w/4f+d, the second thickness is about
c.sub.w/4f-d, and a lateral width of each of the of microfluidic
separation channels is about c.sub.f/2f, where c.sub.w is an odd
multiple of an acoustic velocity of an acoustic wave in the plastic
substrate, c.sub.f is an acoustic velocity of the acoustic wave in
a fluid flowing through each of the plurality of microfluidic
separation channels, f is an operating frequency of the acoustic
wave, and d is a width increment defined by
c.sub.f/16f<d<c.sub.f/4f.
[0011] According to at least one aspect of the disclosure, a method
can include providing a fluid cleansing device. The device can
include a first substrate, a second substrate, and a third
substrate. The first substrate can include a first plurality of
microfluidic channels that are defined in a first face of the first
substrate. Each of the first plurality of microfluidic channels can
include an upstream portion and a downstream portion. The second
plurality of microfluidic channels can be defined in a second face
of the first substrate. Each of the second plurality of
microfluidic channels can include an upstream portion and a
downstream portion. The first substrate can include a plurality of
via channels coupling the downstream portion of the first plurality
of microfluidic channels to the upstream portion of the second
plurality of microfluidic fluid channels. The second substrate can
be coupled with the first face of the first substrate. The second
substrate can define a wall of the first plurality of microfluidic
fluid channels. The third substrate can be coupled with the second
face of the first substrate. The third substrate can define a wall
of the second plurality of microfluidic fluid channels. The first,
second, or third substrate can be configured to couple with a base
substrate comprising one or more acoustic transducers. The method
can include flowing a fluid that includes particles through the
first plurality of microfluidic channels. The method can include
directing, with an acoustic wave generated by the one or more
acoustic transducers, the particles to a first aggregation axis of
each of the first plurality of microfluidic channels.
[0012] The method can include flowing the fluid through a manifold
defined in the first substrate. The manifold can include a network
of biomimetic channels. The method can include flowing the fluid
through a distribution portion of the manifold that is defined in
the first face of the first substrate. The method can include
collecting at least a portion of the fluid at a collection portion
of the manifold defined in the first face and the second face of
the first substrate. The first substrate can include an isolation
slot positioned between each of the first plurality of microfluidic
fluid channels. Each of the one or more acoustic transducers can
protrude perpendicular to a face of the base substrate and into the
isolation slot positioned between each of the first plurality of
microfluidic fluid channels. One or more acoustic transducers can
extend laterally along the base substrate and parallel to the first
substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The skilled artisan will understand that the figures,
described herein, are for illustration purposes only. It is to be
understood that in some instances various aspects of the described
implementations may be shown exaggerated or enlarged to facilitate
an understanding of the described implementations. In the drawings,
like reference characters generally refer to like features,
functionally similar and/or structurally similar elements
throughout the various drawings. The drawings are not necessarily
to scale, emphasis instead being placed upon illustrating the
principles of the teachings. The drawings are not intended to limit
the scope of the present teachings in any way. The system and
method may be better understood from the following illustrative
description with reference to the following drawings in which:
[0014] FIG. 1 illustrates an example system for separating contents
of a fluid.
[0015] FIG. 2 illustrates an example implementation of the system
for separating contents of a fluid.
[0016] FIG. 3 illustrates an example microfluidic flow chamber that
can be used in the system illustrated in FIG. 1.
[0017] FIG. 4 illustrates a wire frame detail of the collection
manifold from the collection manifold illustrated in FIG. 3.
[0018] FIG. 5 illustrates a section view of the wire frame model
illustrated in FIG. 4.
[0019] FIGS. 6-8 illustrate the modeled wall shear rates
experienced within the microfluidic flow chamber illustrated in
FIG. 3.
[0020] FIG. 9 illustrates the wall shear rates experienced in the
transition between via channels and the collection channel.
[0021] FIG. 10 illustrates the fluid velocity experienced in the
transition between the via channels and the collection channel.
[0022] FIGS. 11 and 12 illustrate plots of streamlines through the
transition from the via channels to the collection channels.
[0023] FIG. 13 illustrates a top view schematic of an example
microfluidic flow chamber as can be used in the system illustrated
in FIG. 1.
[0024] FIG. 14 illustrates an isometric view of an example base
substrate to which the microfluidic flow chamber illustrated in
FIG. 13 is to be coupled.
[0025] FIG. 15 illustrate a top view schematic of another example
microfluidic flow chamber as can be used in the system illustrated
in FIG. 1.
[0026] FIG. 16 illustrates an isometric view of an example base
substrate to which the microfluidic flow chamber illustrated in
FIG. 15 is to be coupled.
[0027] FIG. 17 illustrate a cross-sectional view of an example
microfluidic flow chamber as can be used in the system illustrated
in FIG. 1.
[0028] FIG. 18 illustrates a cross-sectional view of an example
microfluidic flow chamber with symmetrical walls as can be used in
the system illustrated in FIG. 1.
[0029] FIG. 19 illustrates a cross-sectional view of an example
microfluidic flow chamber with asymmetrical walls as can be used in
the system illustrated in FIG. 1.
[0030] FIG. 20 illustrates a top view and cross-sectional view of
an example microfluidic flow chamber with asymmetrical walls as can
be used in the system illustrated in FIG. 1.
[0031] FIGS. 21 and 22 illustrates a flow chart of an example
method of cleansing a fluid using the system illustrated in FIG.
1.
DETAILED DESCRIPTION
[0032] The various concepts introduced above and discussed in
greater detail below may be implemented in any of numerous ways, as
the described concepts are not limited to any particular manner of
implementation. Examples of specific implementations and
applications are provided primarily for illustrative purposes.
[0033] FIG. 1 illustrates an example system 100 for separating the
contents of a fluid. In the system 100, blood (or another fluid to
be processed) is removed from a patient 101 via an intravenous line
102. The blood is then pumped to a mixing chamber 104 by a pump
103. In the mixing chamber 104, capture particles are mixed with
the blood. The components of the capture particles are stored in a
reservoir 115. From the reservoir 115, the capture particles are
pumped by a pump 106 into the mixing chamber. From the mixing
chamber 104, the blood and capture particles enter a manifold
system 107. The manifold system 107 distributes the blood and
capture particles to a plurality of separation channels contained
within the microfluidic flow chamber 108. The microfluidic flow
chamber 108 includes one or more piezoelectric acoustic transducers
109. The acoustic waves generated by the acoustic transducers 109
are used to funnel the contents of the blood and capture particles
to specific outlets of the separation channels. In some
implementations, the patient 101 can be replaced with fluid
reservoir or tank. For example, the patient's blood can be
pre-drawn from the patient 101 and then processed by the system 100
at a later time. In another example, the system 100 can be used to
separate the components from a fluid other than blood and the fluid
can be stored in a reservoir and be processed with the system
100.
[0034] As the blood flows through the microfluidic flow chamber
108, the cleansed blood flows to a first outlet 110. After exiting
the first outlet 110, the blood returns to the patient 101, via a
second intravenous line 111. The capture particles and other waste
material removed from the blood exit the microfluidic flow chamber
108 via a second outlet 112. The waste material and capture
particles enter a waste collection unit 113. In the waste
collection unit 113, the capture particles are separated from the
waste material. Once separated, the waste material is discarded and
the capture particles are returned to the reservoir 115 by tubing
114. Once returned to the reservoir 115, the capture particles are
reused in the system to remove additional waste material from whole
blood as it continues to flow through the system 100.
[0035] The system 100, as illustrated, includes a pump 103 for
moving blood from the patient 101 to the mixing chamber 104. In
some implementations, the pump operates continuously, while in
other implementations the pump works intermittently, and only
activates when the level of whole blood in the mixing chamber 104
or manifold falls below a set threshold. In some implementations,
the flow rate of the pump is configurable, such that the rate the
blood exits the patient can be configured to be faster or slower
than if no pump was used. In yet other implementations, no external
pump is required. In this example, the blood is transported to the
mixing chamber 104 by the pressure generated by the patient's own
heart. In some implementations, flow or pressure is monitored in
the network, and these measurements in turn control the pump.
Example pumps can include, but are not limited, to peristaltic
pumps, impeller pumps or any other pump suitable for flowing
blood.
[0036] As illustrated in the system 100, capture particles are also
pumped into the mixing chamber 104. In some implementations, the
capture particles are polystyrene beads or liposomes encapsulating
an acoustically active fluid. The capture particles are described
in greater detail below. A pump 106 pumps the capture particles
from a reservoir 115 to the mixing chamber 104. In the mixing
chamber 104, affinity particles embedded within the surface of the
capture particles bind to undesired particles, cells, or toxins to
be removed from the blood.
[0037] As illustrated in FIG. 1, the capture particles are injected
into the mixing chamber 104. In other implementations, the capture
particles are injected into the manifold system 107 or directly
into the separation channels of the microfluidic flow chamber 108.
In some implementations, the system 100 does not use capture
particles. For example, the components (e.g., red blood cells) of
the fluid to be cleansed may be intrinsically acoustically active.
For example, cells or other objects may have an acoustic contrast
factor sufficiently different than that of the blood or other fluid
and are therefore "acoustically active." These cells or other
objects can be directed with the acoustic transducer 109.
[0038] As illustrated in system 100, the blood containing
undesirable particles and the capture particles enter the mixing
chamber 104. In some implantations, the contents of the mixing
chamber are continuously agitated to improve distribution of the
capture particles throughout the blood and undesirable particles
such that the capture particles bind to the undesirable particles.
In some implementations, anticoagulants or blood thinners are
introduced into the mixing chamber 104 to assist the blood as it
flows through the system 100. In some implementations, the mixing
chamber 104 contains a heating element for warming the contents of
the mixing chamber 104.
[0039] The contents of the mixing chamber 104 then flow into the
manifold system 107, as illustrated by system 100. The manifold
system 107 is described further in relation to FIGS. 3-12, among
others. As an overview, the manifold system 107 flows the blood,
undesirable particles, and capture particles into the inlets of the
plurality of separation channels of the microfluidic flow chamber
108. In some implementations, multiple microfluidic flow chambers
described herein are stacked to process relatively large volumes of
blood or other fluids. The manifold system 107 distributes the
blood to each of the separation channels of the stacked
microfluidic flow chambers. In some implementations, the manifold
system 107 is configured to distribute shear sensitive fluids, such
as blood, to each of the separation channels without damaging the
shear sensitive fluids. In some implementations, the manifold
system 107 is also configured to receive the shear sensitive fluid
from the microfluidic flow chamber 108 after the fluid has flowed
through the microfluidic flow chamber 108.
[0040] The manifold can include biomimetic features. For example,
the manifold can include gradual curving channels rather than right
angles. In some implementations, the biomimetic features can
include channels within the manifold that mimic vascular channels.
For example, the channels split at bifurcations. After a
bifurcation the size of the channel is reduced according to
Murray's Law. In some implementations, the manifold includes trunk
and branch channels, where supply channels flowing to each of the
microfluidic flow chambers branch from a main supply trunk.
Additional information regarding the biomimetic manifold system 107
can be found in U.S. patent application Ser. No. 13/736,685, titled
Compact Hydraulic Manifold Structure for Shear Sensitive Fluids,
which is incorporated herein by reference in its entirety. The
system 100 can also include a collection manifold that condenses
the plurality of separation channels of the stacked microfluidic
flow chambers into the first outlet 111 and the second outlet 112,
which can also be referred to as collection channels. In some
implementations, the system 100 can include multiple collection and
input manifolds that can each collect or supply fluid to a portion
of the separation channels.
[0041] In the system 100, the microfluidic flow chamber 108
contains a plurality of separation channels. The microfluidic flow
chamber 108 and separation channels are described further in
relation to FIGS. 3-20, among others. The capture particles and
undesirable particles are driven with standing acoustic waves to
outlets. In other implementations, the acoustic wave is activated
intermittently. In some implementations, the separation occurs
during a single stage, while in other implementations, the
separation occurs over a plurality of stages. In some
implementations, the microfluidic flow chamber is disposable.
[0042] As shown in the illustrations of system 100, the
microfluidic flow chamber 108 sits atop an acoustic transducer 109.
In some implementations, the system 100 contains a single acoustic
transducer 109, while in other implementations the system 100
contains a plurality of acoustic transducers 109.
[0043] In some implementations, the acoustic transducer 109 is
glued to the microfluidic flow chamber 108. In other
implementations the microfluidic flow chamber 108 is clamped to the
acoustic transducer 109 so the microfluidic flow chamber may easily
be removed from the system. In other implementations the adhesive
material connecting the acoustic transducer 109 to the microfluidic
flow chamber 108 is removable, for example by heating the
adhesive.
[0044] The acoustic transducer 109 imposes a standing acoustic wave
on the separation channels of the microfluidic flow chamber 108
transverse to the flow of the fluid within the microfluidic flow
chamber 108. The standing acoustic waves are used to drive fluid
constituents towards or away from the walls of the separation
channels or other aggregation axes.
[0045] More particularly, the dimensions of the separation channels
are selected based on the wavelength of the imposed standing wave
such that pressure nodes are generated in each of the separation
channels. The capture particles are driven to different positions
within the separation channels based on the sign of their acoustic
contrast factor at a rate which is proportional to the magnitude of
their contrast factor. Capture particles or other elements with a
positive contrast factor (e.g. the formed elements of blood) are
driven towards the pressure nodes within the interior of the
separation channel. In contrast, elements with a negative contrast
factor are driven toward the pressure antinodes.
[0046] Based on these principles, formed elements of blood can be
separated from capture particles (and thus the undesirable
particles bound to the capture particles). For example, capture
particles can be selected to have negative contrast factors, which
is opposite to the positive contrast factors of the formed elements
of blood. Thus, in response to the standing acoustic wave, the
formed elements are driven towards the resulting pressure node
while the capture particles are driven towards the antinodes.
[0047] In other examples, one type of blood cell can be separated
from another because of the differing size, density, or
compressibility of the cell types. For example lymphocytes may be
separated from other white blood cells, red blood cells, and
platelets. In some examples, analytes, diseased cells, or
pathogenic cells, including bacteria, can be separated from normal
blood cells.
[0048] As illustrated in the system 100, the cleansed blood exits
the microfluidic flow chamber 108 at a first outlet 110. From there
the blood is returned to the patient 101 via an intravenous supply
line 111. In some implementations, the blood in the supply line 111
is reheated to body temperature before returning to the patient
101. In other implementations an infusion pump is used to return
the blood to the patient 101, while in the system 100 the pressure
generated in the system by pumps 103 and 106 is adequate to force
the blood to return to the patient 101.
[0049] As illustrated in the system 100, waste material (e.g. the
capture particle and undesirable particles) exit the microfluidic
flow chamber 108 and enter a waste collection unit 113. In some
implementations, the waste collection unit 113 contains a capture
particle recycler. The capture particle recycler unbinds the
undesirable particles from the capture particles. The capture
particles are then returned to the reservoir 115 via tubing 114.
The undesirable particles are then disposed of. In some
implementations, the undesirable particles are saved for further
testing.
[0050] In some implementations, the microfluidic flow chamber 108
can be used for other methods than blood cleansing such as, but not
limited to, apheresis and analytical sample preparation. For
example, in an apheresis process cells, blood plasma, or other
waste is removed from the blood and discarded. A replacement fluid
or suspension can be added back to the blood to replace the volume
lost from the removal of the waste. In an example where the
microfluidic flow chamber 108 is used for sample preparation, the
microfluidic flow chamber 108 can be used to flow extract a desired
fraction of cells or particles from a sample or to remove particles
or cells to leave purified liquid fraction.
[0051] While the system 100 is described above for the in-line
cleansing of a patient's blood, in alternative implementations, the
system 100 can be used to cleanse stored blood or other stored
fluids. For example, the system 100 can be used to cleanse
collected blood for later infusion to help ensure the safety of the
blood or it can be used to prepare blood for analysis.
[0052] FIG. 2 illustrates one example implementation of the system
for separating contents of a fluid. The system includes the
microfluidic flow chamber 108. The microfluidic flow chamber 108
can be positioned against the acoustic transducer 109. The
temperature of the acoustic transducer 109 is controlled via a heat
sink 120 and a peltier device 122. The heat sink 120 and the
peltier device 122 can prevent the acoustic transducer 109 from
overheating the blood flowing through the microfluidic flow chamber
108 and maintain the temperature of the blood in or near
physiological temperature ranges. The system can also include a
heat exchanger 124. The heat exchanger 124 aid in dissipation of
heat generated by the transducer. The acoustic transducer 109, heat
sink 120, and peltier device 122 can be components of a base
substrate.
[0053] FIG. 3 illustrates an example microfluidic flow chamber 108
that can be used in the example implementation of the system
illustrated in FIGS. 1 and 2. The microfluidic flow chamber 108
includes a first substrate 201(1), a second substrate 201(2), and a
third substrate 201(3), which can be generally referred to as
substrates 201. The substrate 201(2) includes a plurality of
separation channels 202. The substrate 201(2) also includes the
distribution manifold 702 and the collection manifold 704, which
can be implementations of the manifold system 107 illustrated in
FIG. 1. The distribution manifold 702 can include a feed channel
205 that can serve as a trunk to the distribution manifold 702. The
feed channel 205 can branch into a plurality of inlets 203 that
form the start of the separation channels 202. The separation
channels 202 can branch to form a plurality of outlets 204. For
example, the separation channels 202 can branch to form a central
and two lateral outlets. The outlets 204 can be a component of the
collection manifold 704. The distribution manifold 702 can be
defined in a first face of the substrate 201(1). The collection
manifold 704 can be defined in the first face and a second face of
the substrate 201(1). Each portion of the collection manifold 704
that is defined in a different face of the substrate 201(1) can
form a collection manifold for one or more of the channels out lets
204. For example, each channel 202 can include one or more outlets
204 that collect the focused particles, which can exit to a
collection manifold on first face of the substrate 201(1) and each
channel 202 can include one or more outlets 204 that collect the
fluid substantially free of the focused particles, which can exit
to a collection manifold on the second face of the substrate
201(1). The distribution manifold 702 can include portions defined
in the first face and the second face of the substrate 201(2). For
example, the portion of the distribution manifold 702 defined on
one face can feed the separation channels 202 with the fluid from
which the particles are to be removed. The portion of the
distribution manifold 702 defined on another face of the substrate
201(2) can feed a buffer fluid into separation channels 202. For
example, the separation channels 202 can include three inlets. The
central inlet can supply a buffer fluid to the separation channel
202. The lateral inlets can supply the blood (or other fluid from
which the particles are to be remove) toward the lateral walls of
the separation channels 202. The acoustic wave can drive the blood
cells (or other acoustically active particles) into the buffer
flowing through the central portion of the separation channel
202.
[0054] The microfluidic flow chamber 108 can include three
substrates 201. In some implementations, the microfluidic flow
chamber 108 can include more than three substrates 201 or can
include fewer than three substrates 201. For example, the
microfluidic flow chamber 108 can include a stacked configuration
that includes a plurality of substrates 201 that include channels
202. The channels 202 of the microfluidic flow chamber 108 can be
machined into the faces of the substrate 201(2). The channels 202
can be created in the face of the substrates 201 using, for
example, direct lithography, photopatternable resists, injection
molding, direct micromachining, deep reactive ion etching (ME), hot
embossing, or any combinations thereof. When the substrates 201 are
coupled together, the top substrate 201(1) can form a wall (e.g., a
ceiling) of the channels 202 machined into the top face of the
substrate 201(2) and the bottom substrate 201(3) can form a wall
(e.g., a floor) of the channels 202 machined into the bottom of the
substrate 201(2). The substrates 201 can be coupled together with,
for example, thermocompression bonding, mechanical coupling (e.g.,
clamps), adhesives, or epoxies.
[0055] In some implementations, the channels 202 can also be
machined into the top substrate 201(1) and the bottom substrate
201(3). In some implementations, the bottom substrate 201(3) can
divided into multiple parts or can be cut away in the region of the
separation channels 202 in order to avoid interfering with the
acoustic properties of the separation channels or to avoid
interfering with the coupling of the transducer to the substrates.
In some implementations the transducer is coupled to a face of the
substrate 201(1) and in others it is coupled to a face of the
substrate 201(2). The channels 202 machined into the top face of
the substrate 201(1) can be fluidically coupled with the channels
202 machined into the bottom face of the substrate 201(1) through
via channels. The via channels can also be referred to as
translation channels, connecting channels, microfluidic channels,
or channels.
[0056] As illustrated, the distribution manifold 702 is machined
into the top face of the substrate 201(2). The distribution
manifold 702 can include the feed channel 205 that branches into
the inlets 203 and the separation channels 202. The separation
channels 202 can then branch into the central and lateral outlets
204. The central outlet 204 can be machined into the top face of
the substrate 201(2) and can feed into the collection channel
206(b) of the collection manifold 704. The lateral outlets 204 can
be coupled with the collection channel 206(a) of the collection
manifold 704. The lateral outlets 204 can be pass through the via
channels to channels machined in the bottom face of the substrate
201(2), which can then feed the collection channels 206(a).
[0057] FIG. 4 illustrates a wire frame model of a detail of the
collection manifold 704 from the collection manifold 704
illustrated in FIG. 3. FIG. 5 illustrates a different view of the
wire frame model illustrated in FIG. 4. The separation channels 202
branch into the central and lateral outlets 204. The neighboring
central outlets 204 can merge and flow into the first collection
channel 206(b) that is machined into the top face of the substrate
201(2). In some implementations, more than two central outlets 204
can merge and flow into a first collection channel 206(b). For
example, between about 2 and about 10, between about 2 and 6, or
between about 2 and 4 central outlets 204 can merge into a first
collection channel 206(b). The collection manifold 704 can include
a plurality of collection layers. For example, 20 central outlets
204 can merge into 10 different collection channels of a first
collection layer, which can merge into 5 different collection
channels of a second collection layer. The collection channels can
continue to merge until a single collection channel remains as an
output. A plurality of collection channels 206(b) can branch
serially off of an outlet trunk as illustrated in FIG. 3.
[0058] The lateral outlets 204 can pass to a collection channel
206(a) formed in the bottom face of the substrate 201(2) by via
channels 802. The via channels 802 can fluidically couple channels
machined into a first face of a substrate 201 to channels machined
into a second face of the substrate 201. For example, the via
channels 802 can coupled the lateral outlets 204 formed in the top
face of the substrate 201(2) with the collection channel 206(a)
formed in the bottom face of the substrate 201(2). The via channels
802 can enable fluid routing in the microfluidic flow chamber 108.
The via channels 802 can enable fluid routing in a substrate 201
such that collection channel 206(b) and 206(a) can cross each other
without intersecting.
[0059] For example, as illustrated in FIG. 4, the middle outlet 204
can continue to flow on a first face of the substrate 201(2) and
into a collection channel 206(b) that is machined into the first
face of the substrate 201(2). The lateral outlets 204 can each flow
into a via channel 802 and into a collection channel 206(a) that is
machined into a second face of the substrate 201(2).
[0060] The via channels 802 can be manufactured by drilling through
the substrate 201 at a predetermined angle 803. The via channels
802 can be laser or mechanically drilled through the substrates
201. The predetermined angle 803 can be between about 10.degree.
and about 80.degree., between about 15.degree. and about
75.degree., between about 20.degree. and about 70.degree., between
about 25.degree. and about 65.degree., between about 30.degree. and
about 60.degree., between about 35.degree. and about 55.degree., or
between about 40.degree. and about 50.degree.. In some cases, the
predetermined angle 803 is about 45.degree.. The predetermined
angle 803 can be less than 45.degree.. The predetermined angle 803
can be selected based on the fluid flowing through the channels.
For example, some fluids (e.g., blood) may be more sensitive to
shear forces or other forms of trauma. For these fluids a smaller
angle can be selected when compared to fluids that are less
sensitive to trauma. The predetermined angle 803 can be selected to
reduce trauma to the blood (or other fluid) flowing through the via
channels 802 and channels 202. The predetermined angle 803 can be
selected to prevent clotting of the blood (or other fluid) at the
transition into and out of the via channels 802.
[0061] FIGS. 6-8 illustrate the modeled wall shear rates
experienced within the microfluidic flow chamber 108. FIG. 6
illustrates the trifurcation from the channel 202 to the central
and lateral outlets 204. As illustrated, the lateral outlets 204
experience a low wall shear rate while the central outlet 204
experiences a relatively higher wall shear rate. FIGS. 7 and 8
illustrate the modeled wall shear rates experienced near the via
channels 802. As illustrated, the via channels 802 experience
relatively greater wall shear rates than the collection channel
206(a). In all cases however, the shear rates are acceptable
because they are below the threshold that would be expected to
damage blood cells. The effective diameters of the central and
lateral outlets and the diameters of the via channels 802 can be
adjusted to improve uniformity of shear throughout the manifolds.
To enable bubbles to pass through the microfluidic chamber 108, the
diameters of the via channels 802 can be larger than the width of
the of lateral outlets 204 and smaller than the width of the
collection channels 206 with which they intersect.
[0062] FIGS. 9 and 10 illustrate the wall shear rates and fluid
velocity, respectively, experienced in the transition between the
via channels 802 and the collection channel 206(a). FIGS. 9 and 10
illustrate the shear and velocity is low in the "backstep" portion
of the transition. The transition can be configured to reduce
trauma to the blood flowing though the transition; however, the
transition is configured such that the shear and velocity are not
too low in the backstep (and other portions of the microfluidic
flow chamber) as to generate areas of stagnation where clots can
form or areas of recirculating flow. In other designs, the via
channels 802 and the channels can be manufactured such that a
"backstep" is not formed.
[0063] FIGS. 11 and 12 illustrate plots of streamlines through the
transition from the via channels 802 to the collection channels
206(a). As illustrated, the transition is configured to not include
recirculating or stagnate flow that can cause clotting or other
issues with flow through the microfluidic flow chamber 108.
[0064] FIG. 13 illustrate a top view schematic of an example
microfluidic flow chamber 108 as can be used in the system 100
illustrated in FIGS. 1 and 2. Also referring to FIG. 3, the
microfluidic flow chamber 108 includes a substrate 201. The
substrate 201 defines a plurality of separation channels 202. Each
of the separation channels 202 includes an inlet 203 and multiple
outlets 204. Each inlet 203 is coupled to a feed channel 205, and
each of the outlets 204 are coupled to a collection channel 206. As
illustrated, the microfluidic flow chamber 108 includes a first
collection channel 206(a) and a second collection channel 206(b).
The substrate 201 also defines a plurality of isolation slots 207.
The acoustic transducers 208 protrude from a base substrate below
the substrate 201 and project through isolation slots 207. The
substrate 201 can be configured to couple with the base substrate.
For example, and also referring to FIG. 3, the substrate 201(3) can
include a plurality of alignment markers that are configured to
receive posts or protrusions from the base substrate.
[0065] The substrate 201 defines the separation channels 202 and
the isolation slots 207. In some implementations, the substrate 201
includes rigid materials such as silicon, glass, metals, or other
materials that establish a high acoustic contrast between the fluid
flowing though the separation channels 202 and the substrate 201.
In other implementations, the substrate 201 includes relatively
more elastic materials, which establish a lower acoustic contrast
between the fluid flowing the separation channels 202 and the
substrate 201. These materials can include thermoplastics, such as,
polystyrene, acrylic (polymethylmethacrylate), polysulfone,
polycarbonate, polyethylene, polypropylene, cyclic olefin
copolymer, silicone, liquid crystal polymer, and polyvinylidene
fluoride.
[0066] The substrate 201 of the microfluidic flow chamber 108
includes multiple separation channels 202. The separation channels
202 are formed into an array of separation channels 202. The array
of separation channels 202 can include between about 2 and about
100, between about 2 and about 50, between about 10 and about 40,
or between about 20 and about 30 separation channels. The inlet 203
of each of the separation channels 202 is coupled to the feed
channel 205 that provides fluid to each of the separation channels
202. The feed channel 205 and the separation channels 202 can be
configured in a trunk and branch configuration. For example, as
illustrated in FIG. 13, the feed channel 205 can narrow as
separation channels 202 branch off the feed channel 205. The trunk
and branch configuration can also include smooth and gradual
transitions between the feed channel 205 and each of the separation
channels 202. The transitions between the feed channel 205 and the
separation channels 202 are configured to reduce or prevent damage
to blood flowing through the microfluidic flow chamber 108 and to
prevent clotting. The feed channel 205 receives fluid from the
manifold system described herein. The separation channels 202 are
configured to branch into multiple outlets 204 toward their
downstream end. As illustrated, the separation channels 202 include
a central outlet and two lateral outlets (generally referred to as
outlets 204). The two lateral outlets of each separation channel
202 are coupled to the collection channel 206(a), and the central
outlet of each separation channel 202 is couple to the collection
channel 206(b). As with between the feed channel 205 and the
separation channels 202, the transitions between the separation
channels 202 and the collection channels 206(a) and 206(b) are
smooth and gradual.
[0067] In some implementations, the capture particles are aligned
toward an aggregation axis that is along a central axis of each of
the separation channels. In these implementations, the fluid
flowing into the central outlet 204 is enriched with the capture
particles, and the fluid flowing into the lateral outlets 204 is
depleted of the capture particles. In other implementations, the
capture particles are aligned toward the walls of each of the
separation channels 202 by the acoustic transducers 208. In these
implementations, the fluid flowing into the lateral outlets 204 is
enriched with the capture particles and the fluid flowing into the
central outlet 204 is depleted of the capture particles.
[0068] In some implementations, the undesirable cells are aligned
toward an aggregation axis that is along a central axis of each of
the separation channels. In these implementations, the fluid
flowing into the central outlet 204 is enriched with undesirable
cell types, and the fluid flowing into the lateral outlets 204 is
enriched with the desired cell type. In other implementations, the
undesirable cells are aligned toward the walls of each of the
separation channels 202 by the acoustic transducers 208. In these
implementations, the fluid flowing into the lateral outlets 204 is
enriched with the undesirable cells and the fluid flowing into the
central outlet 204 is enriched with the desired cell type.
[0069] As illustrated in FIG. 13, the collection channel 206(b) is
in a different plane than the separation channels 202 and the
collection channel 206(a). The collection channel 206(b) is coupled
to each of the central outlets 204 by a fluidic via between the
plane of the separation channels 202 and the collection channel
206(b). In some implementations, the collection channel 206(b) is
in the same plane as the central outlets 204 and the collection
channel 206(a) is in a different plane than the lateral outlets 204
and separation channels 202.
[0070] The microfluidic flow chamber 108 illustrated in FIG. 13
also includes a plurality of isolation slots 207. The isolation
slots 207 are channels that run parallel to the separation channels
202. The isolation slots 207 have a height equal to the thickness
of the substrate 201 and form air gaps through the substrate 201
between adjacent separation channels 202. For example, the
isolation slots 207 can be milled or cut through the substrate 201.
The air gaps between the adjacent separation channels 202, as
provided by the isolation slots 207, isolate the acoustic effects
of waves from the acoustic transducers 208 to specific separation
channels 202.
[0071] In some implementations, the isolation slots 207 run
substantially the entire length of the separation channels 202, and
in other implementations, the isolation slots 207 run along a
length of the separation channels 202 only near the acoustic
transducers 208. Each of the substrates 201 can include isolation
slots 207 or a subset of the substrates 201 can include the
isolation slots 207. For example, the substrate 201(1) and the
substrate 201(2) can include the isolation slots 207. The isolation
slots 207 are between about 100 .mu.m and about 5 mm, between about
200 .mu.m and about 3 mm, between about 300 .mu.m and about 2 mm,
or between about 500 mm and about 1 mm wide. The separation
channels 202 are between about 1 cm and about 10 cm, about 2 cm and
about 8 cm, or about 3 cm and about 5 cm long.
[0072] A plurality of acoustic transducers 208 coupled to the
microfluidic flow chamber 108. The acoustic transducers 208 can
couple with a portion of the substrate 201(2) exposed by a gap in
the substrate 201(3) or the acoustic transducers 208 can be coupled
to the substrate 201(3). The acoustic transducers 208 are, for
example, piezoelectric transducers as described above in relation
to FIG. 1. Each of the acoustic transducers 208 are configured to
imposes a standing acoustic wave on one of the separation channels
202 of the microfluidic flow chamber 108. The standing acoustic
wave is applied transverse to the flow of the fluid through the
separation channels 202. The standing acoustic waves generate
pressure nodes and pressure antinodes within the separation
channels 202 that drive the capture particles towards or away from
the walls of the separation channels 202 or toward other
aggregation axes. The acoustic wave may be applied continuously or
intermittently.
[0073] FIG. 14 illustrates an isometric view of an example base
substrate 210 to which the microfluidic flow chamber 108,
illustrated in FIG. 13, can be coupled. The base substrate 210
includes the acoustic transducers 208, which are powered via
electrical traces 212. The base substrate 210 includes a plurality
of orientation markers 214. The base substrate 210 also include
clamps 216 to clamp a microfluidic flow chamber to the base
substrate 210. In some implementations, the microfluidic flow
chamber 108 can be coupled with the acoustic transducers 208 and
the clamps clamp the acoustic transducers 208 to the base substrate
210.
[0074] The acoustic transducers 208 are mounted to the base
substrate 210. The acoustic transducers 208 project perpendicular
to the base substrate 210. As illustrated in FIG. 13, when the
microfluidic flow chamber 108 is coupled to the base substrate 210
each of the acoustic transducers 208 project into one of the
isolation slots 207. The acoustic transducers 208 are coupled to
one the walls of the of the isolation slots 207, which is a shared
wall with one of the adjacent separation channels 202. For example,
the acoustic transducers 208 can be coupled to the inner walls of
the isolation slots 208 by glycerol, glue, film, gel, or other
material configured to efficiently transfer waves from the acoustic
transducers 208 to the inner wall of the isolation slots 207.
[0075] The base substrate 210 includes a plurality of electrical
traces 212. The electrical traces 212 provide power to and ground
each of the acoustic transducers 208. In some implementations, the
electrical traces 212 terminate in a multi-pin electrical connector
that enable each of the acoustic transducers 208 to be controlled
independently of one another.
[0076] The base substrate 210 also includes a plurality of
orientation markers 214. The orientation markers 214 are raised
pins positioned towards each of the corners of the base substrate
210. The bottom of the substrate 201 illustrated in FIG. 13
includes recesses that mate with each of the orientation markers
214. The orientation markers 214 can ensure the substrate 201 is
properly aligned with the base substrate 201--therefore ensuring
the acoustic transducers 208 are properly aligned with the
separation channels 202.
[0077] The base substrate 210 also includes clamps 216. As
illustrated, the clamps 216 are illustrated in their closed (or
clamped) position. Once the substrate 201 is placed on the base
substrate 210 and properly orientated using the orientation markers
214, the clamps 216 are closed to reversibly couple the substrate
201 to the base substrate 210. In some implementations, the base
substrate 210 includes a clamp 216 on each of its four sides rather
than just two sides as illustrated in FIG. 14.
[0078] FIG. 15 illustrates a top view of an example microfluidic
flow chamber 108. As described above in relation to FIG. 13, the
microfluidic flow chamber 108 includes a substrate 201. The
substrate 201 defines a plurality of separation channels 202. Each
of the separation channels 202 includes an inlet 203 and multiple
outlets 204. Each inlet 203 is coupled to a feed channel 205, and
each of the outlets 204 are coupled to a collection channel 206. As
illustrated, the microfluidic flow chamber 108 includes a first
collection channel 206(a) and a second collection channel 206(b).
The substrate 201 also defines a plurality of isolation slots 207.
The microfluidic flow chamber 108 can couple with or include
acoustic transducers 221. As described below in relation to FIG.
16, the acoustic transducers 221 lie flat on a base substrate (not
shown) below the substrate 201. The acoustic transducer 221 are
coupled to a bottom wall of each of the separation channels
202.
[0079] FIG. 16 illustrates an isometric view of an example base
substrate 222 to which the microfluidic flow chamber 108,
illustrated in FIG. 15, is coupled. The base substrate 222 includes
the acoustic transducers 221, which are powered via the electrical
traces 212. The base substrate 222 includes a plurality of
orientation markers 214. The base substrate 222 also include claims
216 to clamp a microfluidic flow chamber to the base substrate 210.
The clamps 216, orientation markers 214, and electrical traces 212
can be similar to those described above. The acoustic transducers
221 lie flat on the base substrate 222 and are configured to
project an acoustic wave upward into the separation channels 202 of
the microfluidic flow chamber 108. In some implementations, the
microfluidic flow chamber 108 includes recesses to receive the
acoustic transducers 221, enabling the acoustic transducers 221 to
provide an orientation function similar to the orientation markers
214. In some implementations, a single, larger acoustic transducer
221 is coupled to the base substrate 222 rather than a plurality of
smaller acoustic transducers 221.
[0080] FIG. 17 illustrates a cross-sectional view of an example
microfluidic flow chamber 300. The microfluidic flow chamber 300
includes three separation channels 302 that are defined within a
plastic substrate 304. Each adjacent separation channel 302 is
separated by an isolation slot 306. The substrate 304 that defines
the separation channels 302 and the isolation slots 306 sits atop a
base substrate 308. An acoustic transducer 208 is coupled to an
inner wall of each of the isolation slots 306. A heat sink 312 is
coupled to each of the acoustic transducers 208.
[0081] The substrate that defines the separation channels 302 can
have a thickness between about 0.3 mm and about 3 mm, between about
0.5 mm and about 2 mm, or between about 0.5 mm and about 1.5 mm.
The width of the separation channel can be between about 0.2 mm and
about 1.5 mm, between about 0.25 mm and about 1 mm, or between
about 0.25 mm and about 0.75 mm. The depth (or height) of the
separation channels 302 can be between about 0.05 mm and about 1
mm, between about 0.2 mm and about 0.8 mm, or between about 0.2 mm
and about 0.5 mm. The wall thickness of the separation channels 302
can be between about 0.25 mm and about 2 mm, between about 0.5 mm
and about 1.5 mm, or between about 1 mm and about 1.5 mm. The floor
thickness of the separation channels 302 can be between about 0.2
mm and about 2 mm, between about 0.75 mm and about 1.75 mm, or
between about 1 mm and about 1.25 mm. The roof thickness of the
separation channels 302 can be between about 0.2 mm and about 2 mm,
between about 0.75 mm and about 1.75 mm, or between about 1 mm and
about 1.25 mm. The length of the separation channels 302 can be
between about 10 mm and about 200 mm, between about 20 mm and about
150 mm, or between about 30 mm and about 100 mm. The flow rate
through each of the separation channels can be between about 0.01
ml/min and about 1 ml/min, between about 0.1 ml/min and about 0.5
ml/min, or between about 0.1 ml/min and about 0.25 ml/min. The
isolation slots 306 can have a width between about 0.05 mm and
about 1.5 mm, between about 0.25 mm and about 1.5 mm, or between
about 0.5 mm and about 1.25 mm.
[0082] The base substrate 308 of the microfluidic flow chamber 300
is an acoustically inactive substrate. For example, the base
substrate 308 does not substantially transmit waves generated by
the acoustic transducers 208. The acoustic transducers 208 and the
heat sinks 312 are coupled to the base substrate 308. The base
substrate 308 can also include electrical traces for powering the
acoustic transducers 208. In some implementations, the base
substrate 308, with its associated acoustic transducers 208 and
heat sinks 312, is reusable and the microfluidic flow chamber 300
is disposable. A material of high thermal conductivity can be
positioned between the acoustic transducers 208 and the base
substrate 308. This material may be "heat sink compound", a
thermally conducting grease, glycerol, graphite, or compressible
sheets known as "gap pads" in the electronics industry.
[0083] As illustrated in FIG. 17, the acoustic transducers 208 are
coupled to the right inner wall of the isolation slots 306. In the
microfluidic flow chamber 300, each acoustic transducers 208
applies a standing wave 314 to the separation channel 302 to the
right of the acoustic transducer 208. The standing wave 314 travels
from the acoustic transducer 208, through the portion of the
substrate 304 defining the left wall of the separation channel 302,
into the separation channel 302, and then into the portion of the
substrate 304 defining the right wall of the separation channel
302. As illustrated, the isolation slots 306 substantially fail to
transmit the standing wave 314, which prevents the standing wave
314 from meaningfully effecting adjacent separation channels
302.
[0084] The microfluidic flow chamber 300 can be coupled to the base
substrate 308 by glue or by mechanically coupling the microfluidic
flow chamber 300 to the base substrate 308. For example, the
microfluidic flow chamber 300 can be clamped to the base substrate
308. In some implementations, the base substrate 308 and the
microfluidic flow chamber 300 include registration features that
help properly position the substrate 304 on the base substrate 308.
The microfluidic flow chamber 300 can be coupled to acoustic
transducers 208 (or transducer) in a manner to substantially
preserve uniform acoustic energy in each of the separation
channels. The microfluidic flow chamber 300 can be coupled with the
transducers 208 using an ultraviolet (UV) activated epoxy. The use
of UV epoxy can enable accurate setup and positioning of the
microfluidic flow chamber 300 in relation to the acoustic
transducer before the UV epoxy is cured with UV light.
[0085] The heat sinks 312 of the microfluidic flow chamber 300 are
configured to dissipate heat generated by the acoustic transducers
208. For example, the heat sinks 312 are configured to dissipate
enough heat to prevent the acoustic transducers 208 from warming
fluids flowing through the separation channels 302. In some
implementations, the heat sinks 312 are, or include, thermoelectric
coolers. In some implementations, the base substrate 308 includes
fluidic lines that flow into the heat sinks 312 to provide fluidic
cooling to the heat sinks 312.
[0086] FIGS. 18 and 19 illustrate cross-sectional views of example
microfluidic flow chambers. FIG. 18 illustrates a cross-sectional
view of an example microfluidic flow chamber 400 with symmetrical
walls, and FIG. 19 illustrates a cross-sectional view of an example
microfluidic flow chamber 450 with asymmetrical walls. In some
implementations, asymmetrical walls refer to opposite walls of the
separation channels having different thicknesses. FIG. 18
illustrates a single separation channel 401, which may be one of an
array of separation channels, as described above in relation to
FIG. 13. The separation channel 401 is defined by a cover sheet 402
sitting atop a channel layer 403. The cover sheet 402 is coupled to
the channel layer 403, which is coupled to a base substrate 404. As
described above, an acoustic transducer 208 is coupled to an inner
wall of a isolation slot and applies a standing wave 405 to the
separation channel 401.
[0087] The channel layer 403 and cover sheet 402 of the separation
channel 401 are manufactured from, and without limitation,
polystyrene, glass and polyimide, polyacrylic, polysulfone,
silicon, polystyrene, acrylic (polymethylmethacrylate), or other
materials. In some implementations, the channel layer 403 is
manufactured by milling, embossing, and/or etching. After creating
the two layers, the two layers are joined together by
thermocompression, mechanical clamping, adhesive bonding, and/or
plasma bonding. The acoustic transducer 208 imparts the standing
wave 405 at a specific wavelength (.lamda.) across the separation
channel 401. The dimensions of the channel layer 403, cover sheet
402, and separation channel 401 are dependent on the selected
wavelength (.lamda.), as described below.
[0088] As described above, in some implementations, the substrate
sheet is relatively elastic (e.g., when a polystyrene or acrylic
material is used), which provides a relatively lower acoustic
contrast between the fluid flowing through the separation channel
401 and the walls of the channel layer 403. The relatively elastic
materials can form a poor resonator. In implementations using
relatively more elastic materials, the channel width can be defined
using design rules and dimension ratios (with respect to the wall
thickness, wave speed in the fluid and plastic, and/or the
operating frequency) specific to plastics. For example, the channel
width can be defined by a ratio of width of channel to width of
wall, expressed as:
w s w f = n 2 c s c f ##EQU00001## n = 1 , 2 , 3 ,
##EQU00001.2##
which gives:
w f .apprxeq. .lamda. f / 4 = c f 4 .omega. ##EQU00002##
The above dimensions can result in increased performance of driving
particles to pressure nodes in separation channels constructed in
thermoplastics. In the above equation, c.sub.f denotes acoustic
velocity in the fluid flowing through the channel, c.sub.s denotes
acoustic velocity in the wall material, the wall width is w.sub.s,
w.sub.f denotes the channel width, and .lamda..sub.f denotes the
wavelength of the acoustic signal in the fluid.
[0089] In other implementations, where the material of the
substrate is less elastic and forms a good acoustic resonator, the
thickness of the side wall is equal to c.sub.wall/4f, where
c.sub.wall is the speed all of sound in the wall material. The
c.sub.wall for the material is equal to the bulk longitudinal
velocity of sound through the material c.sub.p. In some
implementations, odd multiples of the calculated wall thickness may
be used. The width of the separation channel 401 is equal to about
half the wavelength of the standing wave 405 in the fluid
(.lamda..sub.fluid/2).
[0090] In examples where the substrate is formed from a relatively
more elastic material, the bulk longitudinal velocity of sound
through the material c.sub.p is greater than the speed of sound
through the fluid c.sub.fluid, which is greater than speed of the
reflected wave c.sub.s. In these examples, the acoustic impedance
mismatch between the shear wave and the longitudinal wave is small,
which enables the standing wave 405 to be transferred from the
channel layer 403 to the separation channel 401 with minimal loss
of energy.
[0091] As an example and comparison between designs employing a
weak resonator material and a strong resonator material, assume the
substrate is formed from silicon and the separation channel is
filled with water. In this example, assuming the speed of sound in
water is about 1460 m/s and the acoustic transducer 208 is operated
at about 1.7 MHz, the width of the separation channel would be
about 0.4 mm and the wall thickness (based on a speed of sound in
silicon of about 5968 m/s) would be 0.88 mm. When using a weak
resonator material, such as polystyrene, the separation channel
would be about 0.4 mm, but the wall thickness would be about 1.05
mm (based on a speed of sound in polystyrene of about 1120 m/s) and
the transducer 208 is operated at about 1.0 MHz.
[0092] FIG. 19 illustrates a single separation channel 451, which
may be one of an array of separation channels, as described above
in relation to FIG. 13. The separation channel 451 is defined by a
cover sheet 452 sitting atop a channel layer 453. The cover sheet
452 is coupled to the channel layer 453, which is coupled to a base
substrate 404. As described above, an acoustic transducer 208 is
coupled to an inner wall of an isolation slot and applies a
standing wave 405 to the separation channel 451. As illustrated,
the separation channel 451 is formed off-center with respect to the
channel layer 453, which forms asymmetrically thick walls on either
side of the separation channel 451. As illustrated, the thicker
wall is adjacent to the acoustic transducer 208. In other
implementations, the thinner wall can be adjacent to the acoustic
transducer 208.
[0093] In some implementations, a microfluidic flow chamber with
asymmetrical walls is formed in a substrate that has a relatively
low acoustic impedance compared to the fluid flowing through the
separation channels because it is important that the wave transfer
between the wall material and fluid with relatively little energy
loss. For example, the substrate is relatively more elastic (e.g.,
includes polystyrene or acrylic) than compared to silicon, glass,
or a metal.
[0094] In some implementations, forming the microfluidic flow
chamber 450 with asymmetrical walls enables the capture particles
to be focused along an arbitrary axis of the separation channel
451. This is in contrast to implementations with symmetrical walls
where the capture particles can be aligned with an axis in the
center of the separation channel 401 or along the walls of the
separation channel 401. In one example, the channel 451 dimensions
and channel layer 453 width are calculated as described above with
respect to the device with symmetrical walls, but one of the
sidewalls is thicker than the other by a length equal to 1/4 of the
width of channel 451. In some implementations, the thicknesses of
each of the walls is determined through numerical simulation.
[0095] In some implementations of the microfluidic flow chamber 450
with asymmetrical walls, the thicker wall has a thickness of about
c.sub.w/4f+d, and the thinner wall has a thickness of about
c.sub.w/4f-d. The lateral width of the separation channel is about
c.sub.f/2f. When calculating the thickness of the thicker and
thinner wall c.sub.w is the acoustic velocity of an acoustic wave
in the wall material (or an odd multiple thereof), c.sub.f is the
acoustic velocity of the acoustic wave in the fluid, f is the
desired operating frequency of the acoustic wave, and d is a width
increment defined by c.sub.f/16f<d<c.sub.f/4f. In some
implementations, f is multiplied by a factor of between about 1.5
and about 2.5, between about 1.5 and about 2, or about 1.7.
[0096] FIG. 20 illustrates a top view of an example separation
channel 500 and a cross-sectional view of the separation channel
500 made along cut line A-A. The separation channel 500 includes
asymmetrical walls, where wall 501 is thicker than wall 502. The
separation channel 500 includes an inlet 508, a first outlet 503
and a second outlet 504. A plurality of capture particles 505 flow
down the separation channel 500 in a direction 509 from the inlet
508 to the first and second outlets 503 and 504. A standing wave
506 is applied to the separation channel 500 forming an aggregation
axis 507. In some implementations, the above described devices that
include arrays of separation channels can include arrays of
separation channels with asymmetrical walls.
[0097] The capture particles 505 align at the aggregation axis 507.
The aggregation axis 507 can be formed at a pressure node or
pressure antinode of the standing wave 506. As described in
relation to FIG. 13, devices with symmetrical walls include three
outlets to collect the separated contents of a fluid. For example,
a device with symmetrical walls may align the capture particle
toward the center of the separation channel. A capture particle
dense fluid would then flow into a central outlet of the device,
and a capture particle depleted fluid would slow into the two
lateral outlets. However as described below in relation to FIG. 20,
a device with asymmetrical walls, can be less complex because the
separation channels can include only two outlets.
[0098] As illustrated in FIG. 20, using an asymmetrical wall
design, the aggregation axis 507 is created between the central
axis of the separation channel's lumen and the face of the wall 501
of the separation channel 500. As illustrated in FIG. 20, the
aggregation axis 507 is generated toward the wall 501; however, the
thicknesses of the walls 501 and 502 can be adjusted to place the
aggregation axis 507 at any location in the separation channel 500.
In this example, the capture particle dense fluid can be collected
with a first outlet 503 and the capture particle depleted fluid is
collected with the second outlet 504.
[0099] As illustrated, the first outlet 503 and the second outlet
504 are substantially the same size. In other implementations, the
first outlet 503 and the second outlet 504 are sized differently.
For example, the aggregation axis 507 can be placed closer to the
wall 501, enabling the first outlet 503 to be smaller than the
second outlet 504.
[0100] FIG. 21 illustrates a flow chart of an example method 600 of
cleansing a fluid. The method 600 includes providing a fluid
cleansing device (step 602). A fluid containing capture particles
is flowed through the fluid cleansing device (step 604). The
capture particles are directed toward a first aggregation axis in
each of the separation channels of the fluid cleansing device (step
606).
[0101] As set forth above, the method 600 includes providing a
fluid cleansing device (step 602). The fluid cleansing device can
include any of the microfluidic flow chambers described herein.
Also with reference to FIG. 13, the fluid cleansing device includes
substrate 201 that defines an array of separation channels 202.
Each of separation channels 202 includes an inlet 203 at an
upstream portion and two or more outlets 204 at a downstream
portion of the separation channel 202. Each of the adjacent
separation channels 202 are separated from one another by an
isolation slot 207. An acoustic transducer 208 is positioned within
each of the isolation slots 207 and directs a standing acoustic
wave toward a different one of the separation channels 202.
[0102] The method 600 also includes flowing a fluid through the
fluid cleansing device (step 604). In some implementations, capture
particles are mixed into the fluid before the fluid flows through
the fluid cleansing device. The capture particles are configured to
be acoustically mobile in the presence of a standing wave (e.g.,
the standing wave drives the capture particles to pressure node or
pressure antinode). The acoustic mobility of the capture particles
is tuned by configuring the capture particles to have a specific
size, density, or compressibility. In some implementations, the
capture particles are configured to be substantially more or
substantially less acoustically mobile than other particles in the
fluid. In some implementations, the capture particles include
affinity particles anchored to the outer surface of the capture
particles. The affinity particles are configured to bind to toxins,
pro-inflammatory cytokines, bacteria, viruses, or specific cell
types. In some implementations, cells, such as red blood cells, are
acoustically mobile and may be driven to an aggregation axis
without the use of capture particles.
[0103] The method 600 also includes directing the capture particles
toward a first aggregation axis in each of the separation channels
of the fluid cleansing device (step 606). Also with reference to
FIGS. 13-20 and 3-temp11, each of the acoustic transducers 208
generate a standing acoustic wave within a respective separation
channel. The standing waves forms pressure nodes and/or pressure
antinodes within the separation channel, which form aggregation
axis along the length of the separation channel. As illustrated in
FIG. 20, the capture particles are directed toward the aggregation
axis 507 by the standing wave 506. The aggregation axis 507 is
aligned with the first outlet 503. As the fluid travels down the
separation channel, the capture particles 505 align with the
aggregation axis 507 and flow out the first outlet 503.
Simultaneously, capture particles depleted fluid flows out the
second outlet 504.
[0104] In an example where the capture particles include affinity
particles that bind to a toxin, the capture particles can be mixed
with a patient's blood. The capture particles will bind to the
toxin in the patient's blood. As the capture particles flow down
the separation channel, the capture particles, with their bound
toxins, exit the fluid cleansing device at outlet 503. Blood
substantially free of toxin exits the fluid cleansing device at
outlet 504 and can be returned to the patient. In some
implementations, the capture particles exiting the outlet 503 can
be further processed to separate the capture particles (and toxins)
from the blood flowing out the first outlet 503.
[0105] While the above method 600 is described in relation to
cleaning a fluid, in some implementations, the method 600 can be
used to enrich a fluid. For example, the capture particles may bind
to desired particles (e.g., a specific type of cell), which can be
directed toward an outlet and collected for further use.
[0106] FIG. 22 illustrates a flow chart of an example method 650
for cleansing a fluid. The method 600 includes providing a fluid
cleansing device (step 652). A fluid is flowed through the fluid
cleansing device (step 654). Particles within the blood are
directed toward a first aggregation axis in each of the separation
channels of the fluid cleansing device (step 656).
[0107] As set forth above, the method 600 includes providing a
fluid cleansing device (step 652). The fluid cleansing device can
include any of the microfluidic flow chambers described herein.
Also with reference to FIG. 13, the fluid cleansing device includes
substrate 201 that defines an array of separation channels 202.
Each of separation channels 202 includes an inlet 203 at an
upstream portion and two or more outlets 204 at a downstream
portion of the separation channel 202. Each of the adjacent
separation channels 202 are separated from one another by an
isolation slot 207. An acoustic transducer 208 is positioned within
each of the isolation slots 207 and directs a standing acoustic
wave toward a different one of the separation channels 202.
[0108] The method 650 also includes flowing a fluid through the
fluid cleansing device (step 654). The fluid can be blood. Some
particles within the fluid, such as red blood cells, cells, or
other elements within the fluid, can be acoustically mobile in the
presence of a standing wave (e.g., the standing wave drives the
particles to pressure node or pressure antinode).
[0109] The method 650 also includes directing the particles of the
fluid toward a first aggregation axis in each of the separation
channels of the fluid cleansing device (step 656). Also with
reference to FIGS. 13-20 and 3-temp11, each of the acoustic
transducers 208 generate a standing acoustic wave within a
respective separation channel. The standing waves forms pressure
nodes and/or pressure antinodes within the separation channel,
which form aggregation axis along the length of the separation
channel. As illustrated in FIG. 20, the particles in the fluid
(e.g., red blood cells) are directed toward the aggregation axis
507 by the standing wave 506. The aggregation axis 507 is aligned
with the first outlet 503. As the fluid travels down the separation
channel, the particles align with the aggregation axis 507 and flow
out the first outlet 503. Simultaneously, particles depleted fluid
(e.g., fluid without red blood cells) flows out the second outlet
504.
[0110] The disclosed system and methods may be embodied in other
specific forms without departing from the spirit or essential
characteristics thereof. The forgoing implementations are therefore
to be considered in all respects illustrative, rather than limiting
of the invention.
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